Objective: To analyze the expression of various antigens on the leukemic blasts and to determine the hematological parameters, in Acute Lymphoblastic Leukemia (ALL) patients at presentation. Study Design: Observational study. Place and Duration of Study: King Edward Medical University, Lahore and Hameed Latif Hospital, Lahore, from February 2013 to March 2014. Methodology: Atotal of 50 newly diagnosed and untreated patients of ALL were selected from Mayo Hospital and Hameed Latif Hospital. These patients included both genders and all age groups. Hemoglobin, total leukocyte count and platelet count were determined on hematology analyser-Sysmex-Kx-2I. Blast cell percentage was estimated on Giemsa stained blood smears. Immunophenotyping was done on bone marrow samples by 5 colour flow cytometery on Beckman Coulter Navious Flow cytometer. An acute leukemia panel of 23 antibodies was used. The data was entered and analyzed in SPSS version 22. Results: Of the 50 ALLpatients, 36 (72%) were B-ALL and 14 (28%) T-ALL. There were 18 (36%) children and 32 (64%) adults. T-ALLincluded 22% of the childhood and 31% of the adult cases. Immunophenotypic analysis showed that CD19, CD79a and CD20 were B-lineage specific markers whereas cCD3, CD3 and CD5 were T-lineage specific. CD10 was the most sensitive marker for B-ALL and CD7 was the most sensitive marker of T-ALL. TdT was expressed in 92% B-ALL and 71% T-ALL cases, CD34 in 58% and 43% cases and CD45 in 83% and 100% respectively. High leukocyte count (> 50 x 109/L) was present in 58% cases. Hemoglobin was